"There was a flash of blinding green light and a rushing sound, as though a vast, invisible something was soaring through the air -- instantaneously the spider rolled over onto its back, unmarked, but unmistakably dead"

The Killing Curse (also known as the Avada Kedavra Curse[3]) is a spell that causes instantaneous death and is one of the three Unforgivable Curses. Its incantation is Avada Kedavra.

The only known counter-spell is sacrificial protection, which uses the magic of love. However, one may dodge the green bolt or block it with a physical barrier. The Killing Curse, as an "unblockable" Curse, cannot be intercepted by another spell, except in circumstances of Priori Incantatem, where the caster and his opponent's wands and spells are locked together. An explosion or green fire may result if the spell hits something other than a living target.

Only two wizards are known to have survived blows from this deadly curse: Harry Potter and Tom Riddle. Harry survived two direct attacks: once in 1981 after his mother's self-sacrificing love protected him from Lord Voldemort, and once in 1998 after the curse, cast again by Voldemort, failed to kill Harry, as he was tethered to life by Voldemort himself, due to Lily's blood protection which he took inside himself during his rebirth. Lord Voldemort remained alive after the aforementioned curse from 1981 rebounded and struck him because of his Horcruxes. Voldemort was notorious for using this curse regularly and indiscriminately.

Legal status

Along with the Cruciatus and Imperius curses, the Killing Curse is known as one of the most terrible curses in the wizarding world. After the Wizards' Council was reformed into the Ministry of Magic tighter restrictions were placed on the use of certain kinds of magic. The Killing Curse was deemed by the Ministry to be Dark magic, and, along with the Cruciatus and Imperius curses, were declared "unforgivable" in 1717, with the Killing Curse considered to be the most deadly of the three. Cursing another human with the Killing Curse would carry the punishment of a life sentence in Azkaban.

It should be noted that despite the curse being illegal, references have been made to Aurors using deadly force against opponents, though whether this means they were authorized to use the killing curse specifically is unclear. Despite the circumstances, it is unknown whether the Killing Curse was used by anyone but Voldemort and his Death Eaters during the Battle of Hogwarts. It is also known that use of this curse may go unpunished if there is sufficient evidence that the caster did so under the influence of the Imperius Curse.

Nature

The Avada Kedavra curse is recognisable by the flash of green light and the rushing noise emitted from the caster's wand. When the curse hits a living, organic target it invariably kills them without injury. However, when this curse hits an inanimate target the effect varies: it can produce small fires,[5] small greenish explosions,[6] or explosions of such intensity that can blow up an entire story of a cottage.[7] It is known by most wizards as Lord Voldemort's signature spell. Presumable, it kills it's target by tearing the victim's soul from their body.

However, certain objects, such as the centaur statue of the Fountain of Magical Brethren, managed to block the curse without any visible damage to itself.[8]It should be noted that curse did not terminate the animation of (i.e. "kill") the statue, however, the statue was only animated by magic and so presumably had no real life in him for the curse to take away.

Performance

"Avada Kedavra's a curse that needs a powerful bit of magic behind it - you could all get your wands out and point them at me and say the words, and I doubt I'd get so much as a nosebleed."

The curse requires a great deal of magical talent to perform correctly. In 1994, Barty Crouch, Jr., disguised as Alastor Moody, claimed that, if all of the students before him were to get out their wands and perform it on him at one time, he would probably get nothing more than a nosebleed. However, as his loyalties were with Lord Voldemort, it is unknown to what extent his words were accurate. It is possible to cast the curse non-verbally, as Bellatrix killed a fox without incantation. However, the lack of the incantation may have been for suspense. Whether this is true or not is unknown.[9] Large amounts of concentration is likely required to cast the Killing Curse, which is probably why Death Eaters don't use it as their primary offensive spell (although Thorfinn Rowle did launch the curse repeatedly all over the place during the Battle of the Astronomy Tower).

Signs

The Killing Curse is described as a jet or flash of blinding green light that "illuminates every corner of the room"[10] followed by a rushing sound, which causes the victim instant death. Victims of the Killing Curse are identified by the fact that they simply appear to have dropped dead for no biological reason. Indeed, victims seem "perfectly healthy" apart from the fact that they are dead.[9] This lack of visible injuries is one that had confused Muggles throughout the years of its use, requiring many Ministry of Magic officials to modify memories.

Sensation

Presumably, the Killing Curse does not inflict any pain on its target, since it causes instantaneous death. However, Harry Potter, awaking after a Killing Curse cast by Lord Voldemort hit him, describes the sensation as an "iron-clad punch."

Survivability

"Not pleasant. And there's no countercurse. There's no blocking it. Only one known person has ever survived it, and he's sitting right in front of me."

The Killing Curse is known to be unblockable, as once it strikes the living victim, it almost always results in immediate death. There is "no counter-curse" since it is not possible to revive the dead. However there are some exceptions:

Sacrificial Protection

The most effective method of surviving the Killing Curse is through Sacrificial Protection. The sacrifice of one's life for another, a manifestation of the powerful magic of love, is the most potent defense against the "unblockable" Killing Curse. Harry Potter, was saved by his mother, Lily Evans, lovinglysacrificed herself when she shielded her son with her body[11], making him the first known survivor of this Curse. Harry Potter was the only person known to have survived Avada Kedavra with no ill effects, aside from attaining a scar.

Horcruxes

Lord Voldemort's Horcruxes.

Another defense employed against the Killing Curse is the creation of a Horcrux or Horcruxes. The creation of Horcruxes is a preventive measure, created by a wizard long before he faces an actual Killing Curse attack. However, this is less effective than Sacrificial Protection, since it only allows a little more than the soul of the target to live, while the target's body still dies. If one has Horcruxes, they will not be dead, but they will barely be alive and will be reduced, as Voldemort was when the Killing Curse backfired with his attempt to kill Harry in 1981: to living off another, drinking Unicorn Blood, using the Philosopher's Stone (before it was destroyed), and creating a rudimentary body from Unicorn Blood and Nagini's venom.

Voldemort's Horcruxes tethered his soul to life. The Curse drove his mangled soul from his body and split his unstable soul, leaving him to roam only as a shadowy spirit. If possible, one can make a Regeneration potion to came back to life, but it requires the bone of the father, the flesh of the servant, and the blood of an enemy.

Other

The following are speculations on why only the Horcrux inside Harry Potter, and not Harry himself, had been killed by the Killing Curse in the Forbidden Forest.

Blood within Lord Voldemort

Harry: "But if Voldemort used the Killing Curse, and nobody died for me this time -- how can I be alive?"

Dumbledore: "I think you know. Think back. Remember what he did, in his ignorance, in his greed and cruelty."

Harry: "He took my blood."

Dumbledore: "Precisely! He took your blood and rebuilt his living body with it! Your blood in his veins, Harry, Lily's protection inside both of you! He tethered you to life while he lives [...] He took your blood believing it would strengthen him. He took into his body a tiny part of the enchantment your mother laid upon you when she died for you. His body keeps her sacrifice alive, and while that enchantment survives, so do you and so does Voldemort's one last hope for himself."

During his resurrection, Lord Voldemort used Harry's blood in reconstructing his body. According to Albus Dumbledore, since Harry's blood contained Lily's protection, and Voldemort took this blood for himself, Voldemort had unknowingly tethered Harry to life as long as he himself lives.

As such, the Sacrificial Protection lingering in Harry's blood, which Voldemort took, is similar to but superior to that of a Horcrux's. While a Horcrux requires the preservation of a piece of the soul within an object, blood with Sacrificial Protection required the preservation of the blood within another living entity. While a Horcrux protects the soul from death, blood with Sacrificial Protection is almost as good as Sacrificial Protection; it had the little side effect of Harry feeling an "iron-clad punch" after awakening.

During a discussion with Severus Snape, Dumbledore had specified that it is essential to the plan that Voldemort himself must [kill Harry]. Whether this is because only Voldemort can kill his own Horcrux within Harry, or whether the blood protection would only work specifically with Voldemort (Voldemort being the one from whom Lily had been protecting Harry) is unknown.

Mastery of the Elder Wand

The Elder Wand

Another thing that helped Harry survive when Voldemort tried to kill him in the Forbidden Forest was that Harry was the true master of the Elder Wand, a wand fabled to be unbeatable. Despite Voldemort physically possessing the Elder Wand (having removed it from the tomb of its last master, Dumbledore), he never truly conquered the Elder Wand from its previous owner. Harry, however, did gain its loyalty much earlier: Draco Malfoy "won" the wand from Dumbledore unknowingly, so it was loyal to him, but Harry beat Draco at the Skirmish at Malfoy Manor, so Harry was the true Owner of the wand despite both of them never touching it. The wand wouldn't kill its own master, so when Voldemort tried to murder Harry, the curse only destroyed the part of Voldemort's soul living in Harry and then, when Harry and Voldemort duelled for the final time, the wand backfired and killed Voldemort himself.

Blocking the Curse

Priori Incantatem

The Priori Incantatem effect is when two wands that share the same cores are put into battle against each other. One wand will then force the other wand to repeat its previously-cast spells.

Because of this, an Avada Kedavra Curse can be blocked if a wand that shares the killer's wand's core fires a spell at it: both spells will connect and thus the wizard has been spared by the Killing Curse. However, since wands with twin cores are extremely rare, this method cannot be employed "at will".

Priori Incantatem occurred in the duel between Harry and Voldemort in the graveyard during Harry's fourth year [1]. Voldemort cast the Killing Curse and Harry cast the Disarming Charm, and because their wands had twin cores, Priori Incantantem occurred; Harry was not killed and was able to hold Voldemort off to give him time to escape.

Fawkes the Phoenix ate the Killing Curse meant for Dumbledore, bursting into flames and then regrowing from the ashes

Phoenixes

Phoenixes are semi-protected from the Killing Curse, due to them being immortal. In 1996, Fawkes swallowed one intended for Albus Dumbledore, causing him to burst into flame and die instantly. However, he then was reborn from his ashes.[8]

Stunning Spell

The spell can be directly countered using a Stunning Spell, in which case red and green jets of light will meet and create multi-coloured sparks. Since neither spell is able to reach its intended target, neither will have any effect.

Other Targets and Dodging

If another target is placed between the caster and the targeted individual, then the new target will take the hit of the Killing Curse, which may simply result in an object being destroyed or damaged. One can also avoid the effects simply by dodging or if the caster has poor aim, as with many attacking curses of this type, the spell must be directly targeted at the intended victim.

Etymology

Avada Kedavra is either based on the Aramaic עַבְדָא כְּדַברָא, avda kedavra, meaning "what was said has been done", or on the Aramaic אַבַדָא כְּדַברָא, avada kedavra, meaning "be destroyed at this word". J. K. Rowling seemed to support the second theory as the source, during an audience interview at the Edinburgh Book Festival on 15 April, 2004, where she had this to say about the spell's etymology: "Does anyone know where avada kedavra came from? It is an ancient spell in Aramaic, and it is the original of abracadabra, which means 'let the thing be destroyed.' Originally, it was used to cure illness and the 'thing' was the illness, but I decided to make it the 'thing' as in the person standing in front of me. I take a lot of liberties with things like that. I twist them round and make them mine."[12]
This phrase is also the origin of abracadabra, which, like hocus pocus, is used by magicians as a magic word when they perform tricks.[13]

"Kedavra" also sounds very similar to the English word cadaver, which means "corpse," and derives from the Latin cadere, "to fall."[14]

Behind the scenes

The biological reasons for the victim's death have never been fully explained. It is possible that the victim's internal organs cease function, or that once the spell hits a person's body, it simply kills every living cell in the victim's body. It could also cause sudden brain death, simply stopping the progress of every electrical synapse in the brain simultaneously by draining all potential energy there. In addition to this, it is possible that it causes a person's soul to "pass on", and leave the body, similar to when the body dies naturally, and the soul passes on into whatever afterlife there may be.

In the film adaptation of Harry Potter and the Chamber of Secrets, Lucius Malfoy says "Avada" at Harry Potter after he unwillingly frees Dobby. Dobby knocks Lucius backwards with magic to protect Harry, and he does not finish the incantation. The part of the incantation shown, for plot reasons, was not represented in the subtitles. However, on the DVD if the audio is set to Spanish, Lucius says what it sounds like "Arara" in a more of a shouting way than hissing. It should be noted that Lucius Malfoy saying "Avada" was an ad-lib by his actor Jason Isaacs, as the script did not specify which curse he was supposed to use in the scene, so he used the first curse that came to his mind.[citation needed]

In Harry Potter and the Prisoner of Azkaban, Sirius Black and Remus Lupin intended to kill Peter Pettigrew for his betrayal of James and Lily Potter. It is unknown how they wanted to do it, possibly by the use of this curse. If it would have been used, Peter would have died the same way as his former friends.

Out of the three, the Killing Curse is the only Unforgivable Curse that Harry did not use.

After Harry Potter survived a second killing curse, he described it as having left a bruise that felt like an "iron-clad punch."

While the curse is noted to be unblockable, in Part 2 of the final film Harry is seen blocking it many times from Voldemort, and Bellatrix blocking it from Molly Weasley four times despite it being unblockable with a Shield Charm. Therefore the films portray it as blockable. Additionally, the seventh book describes a scenario in which jets of red and green light intersect and form multi-coloured sparks, suggesting that there was in fact a method of blocking. It is possible that the fake Moody was referring to specific defences, such as a Shield Charm or protecting one's mind.

The Killing Curse is not the only spell that can cause death to a living creature. Other spells may cause grievous injury, such as Fiendfyre, Sectumsempra, Antonin Dolohov's curse, the Blasting Curse, or an overuse of the Stunning Spell. Furthermore, it's likely that many spells can potentially cause death under certain circumstances, such as Impedimenta off a cliff, Diffindo across the throat, etc. However, this is the only spell whose sole and primary application is to cause death.

In Harry Potter and the Deathly Hallows: Part 2, the Killing Curse rebounds on Voldemort during his duel with Harry by the green light of the curse emitting through the crack in the Elder Wand, causing Voldemort's hand to turn black and spread, leading to his death.